Decondensation of<i>Xenopus</i>sperm chromatin using<i>Saccharomyces cerevisiae</i>whole-cell extractsThis paper is one of a selection of papers published in this Special Issue, entitled The Nucleus: A Cell Within A Cell.
Bibliographic record
Abstract
Biochemical studies using highly condensed Xenopus sperm chromatin and protein extracts prepared from multiple systems have lead to the identification of conserved proteins involved in chromosome decondensation. However, mutations to these proteins are unavailable as the systems used are not amenable to genetic studies. We took a genetic approach to isolating chromosome decondensation mutants by incubating Xenopus sperm chromatin with whole-cell extracts prepared from the Hartwell library of random temperature sensitive (ts) yeast cells. We show that decondensation of Xenopus sperm chromatin using wild type yeast extracts was rapid, ATP- and extract-dependent, and resistant to heat, N-ethylmaleimide, protease K, RNase A, and micrococcal nuclease. From 100 mutant extracts screened, we obtained one strain, referred to as rmc4, that was chromosome decondensation defective. The mutant was slow growing and exhibited germination defects. Low concentrations of rmc4 extract would eventually decondense sperm heads, and fractionation of the mutant extract produced a decondensation competent fraction, suggesting the presence of an overactive inhibitor in rmc4 cells. We performed a multicopy suppressor screen that identified PDE2, a gene encoding a protein that inhibits protein kinase A (PKA) activity. As PKA was previously shown in human cells to maintain condensed chromatin, our results suggest that PKA activity is elevated in rmc4 cells, causing a decondensation defect. Thus, our experiments reveal that yeast encodes an evolutionarily conserved chromosome decondensation activity that can be genetically manipulated.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".